Recent years have seen the development of a biometric authentication technique for authenticating a user of an apparatus or a system based on a biometric image representing the user's biometric information such as the user's palm or finger vein pattern or the user's fingerprint or palm print. A biometric authentication device using such a biometric authentication technique acquires, as an input biometric image, a biometric image representing, for example, the biometric information of the user who intends to use the biometric authentication device. Then, the biometric authentication device compares the user's input biometric information represented by the input biometric image with registered biometric information, i.e., biometric information prestored in the form of a biometric image for the corresponding registered user. When the result of the comparison indicates that the input biometric information matches the registered biometric information, the biometric authentication device authenticates the user as being a legitimate registered user. The biometric authentication device then permits the thus authenticated user to use the apparatus in which the biometric authentication device is incorporated or some other apparatus connected to the biometric authentication device.
The direction, at the time of registration, of biometric information relative to a sensor acquiring the image representing biometric information may be different from the direction of the biometric information at the time of matching. Even for the same characteristic structure included in biometric information, the position and direction of the structure on a biometric image acquired at the time of matching is different from the position and direction of the structure on a biometric image acquired at the time of registration when the directions of the biometric information on these images are different from each other. Thus, when matching input biometric information with registered biometric information, the biometric authentication device attempts to find a position where the input biometric information best matches the registered biometric information while rotationally scanning at least one of the image of the biometric information acquired at the time of registration and the image of the biometric information acquired at the time of matching so that the direction of the biometric information acquired at the time of the registration substantially matches the direction of the biometric information acquired at the time of the matching. However, a wide rotation angle range to be scanned increases not only processing time but also the probability (referred to as a false acceptance rate) that, even when a user carrying input biometric information is different from a registered user registered biometric information, the biometric authentication device mistakenly authenticates the user as the legitimate registered user. Thus, for example, the biometric authentication device is operated such that an allowable range is preset for angular difference between the direction of the biometric information acquired at the time of the registration and the direction of the biometric information acquired at the time of the matching, and that a body part carrying the biometric information is held over the sensor so that the angular difference falls within the allowable range.
However, when the sensor is fixedly installed, for example, when the sensor is installed in an automated teller machine or into a palm rest unit of a notebook personal computer, the sensor is located, for example, at a right end or a left end of such apparatus. This is because, in such an apparatus, a display device or an input device such as a keyboard or a touchpad, which is a main user interface, is located in a central portion of the apparatus for the user's convenience and because the end of the apparatus is the only place where the a sensor for biometric information input can be located.
When the sensor is located at the right end or left end of the apparatus and the user holds a body part located closer to the sensor, for example, the user's right hand, which is closer to the sensor located at the right end, over the sensor in a natural posture, the direction of the body part is substantially parallel to a vertical direction of the sensor (i.e., the direction from the near side to the far side). On the other hand, when the user holds a body part located farther from the sensor, for example, the user's left hand, which is farther from the sensor located at the right end, over the sensor in a natural posture, the direction of the body part is rotated through about 90° from the vertical direction of the sensor. Thus, the angular difference between the direction of the body part and the direction of the sensor may deviate from the set allowable range, the user may not be authenticated. Furthermore, when the user holds the body part located farther from the sensor over the sensor in an unnatural posture so as to make the direction of the body part substantially parallel to the vertical direction of the sensor, the body part may be twisted or significantly tilted in any direction to the sensor. In such a case, the biometric information captured on the biometric image is distorted. Therefore when such a biometric image is used for a biometric authentication process, authentication accuracy may decrease.
Thus, various techniques have been proposed to solve the problems as described above (see, for example, Japanese Laid-open Patent Publication No. 2007-65900, Japanese Laid-open Patent Publication No. 2001-243465, and Japanese Laid-open Patent Publication No. H7-110860).
In an example of such known techniques, a rotation mechanism is provided in a coupling unit between a biometric authentication device and an automatic dealing device. When a user operates the biometric authentication device, the rotation device rotates the biometric authentication device so that the user can easily use the biometric authentication device.
Furthermore, in another example of the known techniques, a palm position detecting device detects the lateral direction and the left, right, top and bottom ends of the palm in an image of the palm side of the hand to detect the position of the palm in the image, and rotates the image based on the lateral direction of the palm so as to allow coordinates to be detected.
In yet another example of the known techniques, a biometric information authentication system prestores biometric information on each registered user and corresponding angle information. The biometric information authentication system utilizes the angle information to judge whether or not read biometric information matches the stored biometric information.